The production of anhydrides involves partial oxidation of an appropriate hydrocarbon in the presence of a suitable catalyst. Commercial maleic anhydride production employs feeds of an appropriate gaseous reactant stream such as butane, butene or benzene into a partial oxidation reactor where, in the presence of air/oxygen and a suitable catalyst, maleic anhydride is produced with lower amounts of other oxygenates and carbon oxides. In most cases, butane is the preferred feedstock. When butane is used as the starting raw material, the reactor is often a fluidized bed reactor which includes a separate air injection conduit for introduction of air into the fluidized bed.
To provide oxygen for the conversion of butane to maleic anhydride, the prior art has suggested the addition of oxygen or oxygen-containing gas directly to the feed flow or as a separate feed to the reactor. Such teachings can be found in U.S. Pat. No. 3,899,516 to Dickason, U.S. Pat. No. 4,668,802 to Contractor, U.S. Pat. Nos. 4,987,239 and 5,126,463 to Ramachandran et al. None of the aforesaid patents provides any teaching that an oxygen deficiency can occur in a fluidized bed reactor at the point of reactant feed introduction. Dickason teaches adding substantially pure oxygen directly to the reactor at high butane concentrations. Contractor teaches the use of a transport bed with air, oxygen enriched air, or oxygen in the regeneration zone. Both Ramachandran patents teach that when pure oxygen feed is present in the partial oxidation reactor, that a gaseous flame suppressor mixture be utilized, e.g., carbon dioxide or a substantially unreacted hydrocarbon. As a result, both Ramachandran patents provide further apparatus downstream from the partial oxidation reactor to recover and recycle the carbon dioxide and unreacted hydrocarbon feed.
U.S. Pat. No. 3,661,165 to Rainbird et al. discloses a sparger valve for mixing oxygen with gaseous hydrocarbons in a process stream. The Rainbird et al. sparger valve includes a number of jets facing downstream within the hydrocarbon gas flow. The jets introduce oxygen at a jet velocity that is substantially higher than the velocity of the hydrocarbon gas. Variations in oxygen mass flow are achieved by varying the area of the jet orifices, while maintaining a predetermined pressure drop across the orifices.
U.S. Pat. No. 3,702,619 to Son discloses a process and apparatus for dispensing an gaseous stream into another gaseous stream in an inline mixing apparatus.
U.S. Pat. No. 5,356,213 to Arpentinier describes a further sparger design which is positioned coaxially with respect to the axis of a channel containing a feed stream. Radial vanes are employed in the sparger to inject gas in a substantially radial direction towards the outside of the feed flow so as to enable a mixing of the injected gas with the feed flow gas.
The above noted prior art includes no teaching of fluidized bed reactor performance penalties which occur as a result of oxygen deficiencies at points of feed stream introduction. Further, the prior art, while including teachings regarding the introduction of oxygen-bearing gases at various points in a process, includes no teachings of how such an introduction can be accomplished in a manner to assure process safety.
Accordingly, it is an object of this invention to provide an improved system for enabling an oxygen bearing gas to be combined with a gaseous reactant feed flow to a fluidized bed reactor.
It is another object of this invention to provide an improved system and method for combining an oxygen-bearing gas and gaseous reactants in a manner to avoid explosions, deflagration or other anomalous effects in the process.
It is yet another object of this invention to provide an improved method and system for addition of oxygen to butane in a fluidized bed reactor wherein oxygen deficiencies at feed flow entries are voided.